Antenna



Feb. 13, 1951 T, H, CLARK 2,541,037

ANTENNA Filed April 19, 1946 INVENTOR. TREVOR C'ZflRK ATTORNEY Patented Feb. 13, 1951 UN-I 'ITED STATES @iFF ANTENNA- Trevor Clark,.,Bloonton, N. J., assignor to Fed eral. Telephone and Radio Corporation, New. York, N; YT, a: corporationofDelaware ApplicatiomAprililB, 19465. swarm. coasts (o1. zen-33) Claims;

This; invention. relates to: antennas: and; more particularly to antennas employing a surface memberasaa radiator or: collector.

the. applicationof wide band antennas for ultra high frequencies, it has; been the custom to provide; a; dipole collecting element. which. is mounted; andtspaced in respect to' al reflection element, thedipole being; connected.v tov a transmission. linein: such? a way that the impedance of the transmission. line: is. substantially equalled by the impedance; or the collecting element or antenna in: combination: with: the reflecting sur face. If such a. reflector comprised ofa: sheet of metal is interposed. in; an; electromagnetic field, currents will flow: therein". The magnitude of such currents wilLdependupomthecharacteristics of; the conductor; inithis case. the reflector, such as conductivity... skin effect, dimensions of. the conductor,; wave: lengths of the radiation-1 and the position. of. the'reflector-with respect-to:thewvector quantities of. the e1ectromagnctic.v field. Accord ing. to my invention, if; reflection ispertec.t,. that iswhenano energyds absonbed'irrthe' metallic surface' and thereby: the field at. the surface of the refiectorbecomea zero,. no antenna; need be used, provided. that the reflector is large in: comparison. to the; wavelength, the; reflector. being, energizedl directl inthe. same modes: asit would; be by radiation. from. a. special 1. antenna.

It is an object. of. the: invention to provide an antenna which utilizesanextended surface: similar to. areflectin'g surface as a primary radiator or collector and eliminates the requirement for the usual collecting element...

It is another objecttolprovide a reflector type surface antenna which is large in. comparison to the wave length of the radiation employed.

It is still anotherobject to provide an antenna wherein the energy in the transmission lineis substantially equal to the energy of theifleldinterceptedby'the antenna.

Asti'll further object is to: provide an. antenna of the extended surface type: which is: fed: by means of a. transmission: line connected to; spaced points on the surface, the spacing of the trans-- mission line conductors adjacent the surface being such as to secure maximum transfer f the energy from the reflector sheet in respect to the transmission line over a wide band of frequencies.

A still further object is to provide an antenna of the reflecting surface type which has a substantially constant impedance character over a wide range of frequencies.

In accordance with my invention, I provide an antenna in the form of a sheet with a surface similar to a metallic reflecting surfacewhich is preferably constructed or composed so asto possess large electrical dimensions and which is fed from a transmission line coupled to two points on the surface; the spacing of. the two pointslbeing determined by the transmission line impedance and:the-characteristic of the reflecting sheet.. The transmission line may be coupled to the sheet in a variety of methods, such as direct, inductive or capacitiv coupling. The extent of the sheet from an electrical point of view may be enlarged by using a; surface havinga large electrical resistance or provided with marginal wave-traps.

These and other features and objects of the invention will. be: best understood from the following description of an embodiment thereof, reference being had to the drawings, iniwhichz Fig. I is: a view in perspective of an antenna in accordance with the invention;

Figs. 2 and 2A represent a view in perspective.

and in. elevation respectively, of a capacitively coupled antenna;

Fig. 3 is a perspective view of an inductively coupled antenna; Fig. 3A is adetail of an alternatirve ofiFig. 3;,and

Fig.- 4: a view in perspective showing a combinatiorr of. capacitive and inductive coupling- Referring to the figures, the antenna, in all of the cases illustrated; is comprised of a reflector type surface l which is fed from a transmissionline 2 having. two conductors coupled to two: points 3. and 4' ofthe; surface 5. The points 3 and 4 are spaced apart a distance such as to make the impedance between the two points equal to the: impedance of the transmission line. Thatqis to say, the distance is a function of the physical and electrical characteristics of the refleeting surface l which. determine th imped ance thereof. The various figures indicate alternative methods of coupling the line to the surfacet Ilhus, a direct connection of the line tothe surface is shown in Fig. l.

A capacitive coupling, is: indicated in. Figs. 2 and: 2a by bringing; two conductors of; the: line 2 to two plates 5 and t which are spaced away from and disposed parallel to the surface I, the two conductors being brought out thru suitable openings in the surface.

In Fig. 3, the two conductors of the line 2 are coupled to the surface 4 on the far side thereof and include inductive loops 1 and 8, the conductors being brought out through two apertures 9 and Ill in th surface I.

In Fig. 4, the coupling is a combination of meth- 3 ods illustrated in Figs. 2 and 3 in that the two conductors are brought in through two openings II and I2 in the surface and connected to a capacitive coupling plate l3 connecting the two conductors which also form slight loops as at M and I5.

In the preferred form, the antenna surface I is 7 preferably composed of a material which renders it highly resistive so as to give it a large electrical size in comparison to the wave lengths used to make the currents flowing therein substantially uniform over the surface. The resistivity of such material may be made sufliciently high so as to produce the effect of a conductor of infinite extent. Effects of this sort may be achieved by the use of graphite or by oxidized steel or other materials having a high resistance to high frequency currents.

In another method, wave traps may be used along the edges of the surface whereby for given wave lengths, the electrical extent of the surface is effectively considerably enlarged. With the space in between the two points at which the transmission line is coupled to the'surface being .chosen to present, an impedance which is equal to the impedance of the transmission line, a maximum transfer of currents from and to the conducting sheet to the transmission line over energy in respect to said surface, and a coupling.

' means including a capacitive coupling between a Wide band of frequencies is made possible. The

radiation pattern of the antenna will be substantially circular and in the ideal case, that is where the sheet or surface is of practically infinite electrical extent, is entirely unidirectional. In the case where the current flow in the surface is uni- 5 I form, which is, of course, the ideal one, the lines of distribution of the currents approximates that of the lines of force of opposed magnetic poles, or such as might be found in respect to the free ends of the two conductors of a transmission line in space.

The inductive loops as shown at i and B in Fig. 3 of the transmission line may be further provided with shields which are provided with a gap intermediate the ends thereof in order to improve the circuit balance of the conductors in accordance with balance-to-unbalanced coupling methods generally used. This is shown in Fig. 3A. a

It will be thus seen that I have provided an effective unidirectional antenna which eliminates theintermediary of a dipole and provides for an efficient transfer of energy as between a transmission line and the antenna. 7

While I have described above the principles of this invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of this invention as set forth in the objects hereof.

I claim:

1. An antenna for simulating the radiation pattern of an antenna and a special reflector comprising a substantially continuous conductive surface member having along the surface of said said conductors and said surface, coupling said line to an intermediate position on said surface at spacings providing an impedance match with said line for causing said surface to radiate.

2. An antenna according to claim 1, wherein said capacitive coupling comprises capacitor plate means spacedv from said surface for terminating said conductors.

3. An antenna according to claim 2, wherein said capacitor plate means includes a capacitor plate joining said two conductors in front of said surface.

4. An antenna for simulating the radiation pattern of an antenna and a special reflector comprising a, substantially continuous conductive surface member having along the surface of said member an extent in every direction which is large in comparison with the Wave length used, a transmission line having two conductors of a given total impedance for transferringradiant energy in respect to said surface, and means including an inductive coupling between said conductors and said surface, coupling said line to an intermediate position on said surface at spacings providing an impedance match with said line for causing said surface to radiate.

5. An antennafor simulating the radiation of an antenna and a special reflector comprising a substantially continuous surface member having in every direction of the surface of said member a dimension which is large in comparison to the wave-length used, a transmission line having two conductors and a given total impedance for transferring radiation energy in respect to said surface, and impedance means coupling said line to an intermediate position on said surface at spacing providing an impedance matching with said line for causing said member to radiate, said. impedance means including a capacitive plate joining said two conductors in front of and spaced 7 from said surface and loops connecting said two conductors to said capacitive plate for providing inductive and capacitive coupling between said conductors and said surface.

TREVOR H. CLARK.

REFERENCES orrEn The following references are of record in the 

